Durham E-Theses I. Some studies on Boronium salts; II. the coordination chemistry of Beryllium borohydride Banford, L. How to cite: Banford, L. (1965) I. Some studies on Boronium salts; II. the coordination chemistry of Beryllium borohydride, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/9081/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk 2 I. Some Studies on Boronium Salts II. The Coordination Chemistry of Beryllium Borohydride by L. Banford. thesis submitted for the Degree of Doctor of Philosophy in the University of Durham. June 1963. ACKNOWLEDGEMENTS. The author wishes to express his sincere thanks to Professor G.E. Coates, M.A., D.Sc, F.E.I.C., under whose direction this research was carried out, for his constant encouragement and extremely valuable advice. The author is also indebted to the General Electric Company Limited for the award of a Research Scholarship. MEMORANDUM The work described in this thesis was carried out at the Science Laboratories of the University of Durham between October 1962 and May 1965» an^ nas no* been submitted for any other Degree. All the work described is the original work of the author, except that acknowledged by reference. The work undertaken by the author consisted of two separate investigations, the results of which are incorporated in parts one and two of this thesis. Part of the work has been the subject of two publications in the Journal of the Chemical Society. (J . ,196^,356<*-» J • * 1965,5591) . SUMMARY. PART I: Some studies on boronium salts. Diphenylbipyridylylboronium salts and also the diphenyl- o-phenanthrolineboronium salts are relatively resistant to hydrolysis, and undergo metathetical reactions in aqueous solution The colourless, very sparingly soluble hydrated nitrate, as well as the perchlorate and hydrogen sulphate, are readily precipitated from aqueous solution. The colours of the iodides and some other + + + salts of the (Fh2bipyB) , (Ph2phenanB) , and (n-Bu2bipyB) cations are considered to be due to charge-transfer transitions between the anion and cation. The yellow colour of bipyridylyl- phenylenedioxyboronium perchlorate is attributed to intra-ionic charge-transfer, and the red colour of bisdimethylaminobipyridylyl boronium tetraphenylborate may also be due in part to intra- ionic charge-transfer. The ultra-violet and visible spectra of several coloured boronium salts have been obtained in solvents of varying dielectric constant. PART II: The coordination chemistry of beryllium borohydride. Beryllium borohydride forms an isobutylamine complex, L (Be(Bu" NH2)2f) (BH^).,, which can be sublimed at low pressure and is nearly insoluble in diethyl ether. Reactions of the borohydride with some ethers are discussed. Several liquid 1:1 adducts of the type, L.BeB_H (where L = Et_0, Me,P, Me_PH, Et,p, Me,N, do Q d ~> d 5 5 Me2NH), have been prepared and their formation has been followed tensimetrically. The adducts are monomeric in benzene solution. Triphenylphosphine forms a 1:1 adduct which is monomeric in benzene solution and decomposes when heated with the formation of triphenylphosphine-borane. Reaction with 2 moles of triphenylphosphine gives only the 1:1 adduct at room temperature, but between 100-180°, triphenylphosphine-borane is formed in high yield together with beryllium hydride, which is contaminated with some strongly held triphenylphosphine-borane. The main feature of the infrared spectrum of the best specimen of beryllium hydride prepared by this method consists of a broad absorption centred on 1758cm Trimethylphosphine reacts rapidly at room temperature to form the liquid adduct, and then slowly reacts with a further mole of phosphine to give a solid product of overall composition (Me^Pj^Bel^Hg, from which trimethylphosphine-borane can be sublimed at room temperature* TABLE OF CONTENTS. Page. Part I Some studies on boronium salts. 1 - 76 INTRODUCTION 1 - 37 Object of investigation 1 Cationic organo-boron compounds:-Boronium salts 2 Anionic compounds of boron 17 References to Introduction 32 EXPERIMENTAL 38 - 63 Analytical methods 39 Preparation of starting materials 42 Diphenylborinic acid: - from trimethoxyboroxine and phenylmagnesium bromide 42 - from dichlorodiphenylaraino-borane and:, phenylmagnesium bromide 43 Diphenylboron chloride 44 o-Fhenylenedioxyboron chloride 45 EXPERIMENTAL RESULTS 46 Preparation of 2,2»-bipyridylyldiphenyl- boronium salts 46 = 49 Preparation of 2,2'-bipyridylyldibutyl- boronium iodide 49 Preparation of o-phenanthrolinediphenyl- boronium salts 50 - 51 Page Reaction between diphenylboron chloride and ethylenediamine 51 Reaction between diphenylboron chloride and N,N,N;N'-tetramethylethylenediaraine 52 Reaction between o-phenylenedioxyboron chloride and bipyridyl 52 Reaction between bisdiinethylaininoboron chloride and bipyridyl 51*- Ultraviolet and visible absorption spectra of some boronium salts 56 - 60 Tables of infra-red spectra 61 - 63 DISCUSSION Gk - ?6 References to discussion 76 Part II The coordination chemistry of Beryllium Borohydride 77 - 180 INTRODUCTION 77-126 Object of investigation 77 Preparation of metal borohydrides 77 Structure and reactions of metal borohydrides 90 Reactions of alkali-metal borohydrides 98 Reactions of covalent metal borohydrides 110 References to Introduction 119 Page EXPERIMENTAL 12? - 156 Apparatus and techniques 127 Preparation of starting materials:- - Beryllium chloride 130 - Lithium borohydride 130 - Beryllium borohydride 131 Analytical methods 133 EXPERIMENTAL RESULTS Ether complexes of beryllium borohydride 135 Preparation of beryllium borohydride adducts:- Tetrakisisobutylamineberyllium borohydride 136 Triphenylphosphineberyllium borohydride 137 Triethylphosphineberyllium borohydride 138 Trimethylphosphineberyllium borohydride 139 Dimethylphosphineberyllium borohydride 1^0 Diraethylamineberyllium borohydride 140 Ligand displacement from beryllium borohydride adducts 1^0 Preparation of beryllium hydride from phosphine adducts of beryllium borohydride 1^1 Tensimetric titration of beryllium borohydride with donor molecules 1^5 Attempted preparation of bistrimethylphosphine- beryllium borohydride 150 Attempted alkyl-hydrogen exchange reaction between trimethylborane and beryllium borohydride 153 Attempted preparation of chloroberyllium borohydride etherate 15^ Tables of infra-red spectra 155 DISCUSSION 157 - 180 References to Discussion 179« Part I. INTRODUCTION INTRODUCTION. Object of investigation. The literature contains many references to boronium salts, but it is only recently that these salts have attracted serious study. In general, the unusual chemical stability shown by some of these compounds has not been realised, and in this present work a detailed study has been made of the preparation and properties of the bipyridylyldiphenylboronium salts. During the course of this work it was found that several of these salts were coloured in the solid state, but in solvents of high dielectric constant the salts dissolved to give colourless solutions. The u.v. and visible spectra of these salts have been recorded:- in solvents of varying dielectric constant, and the results interpreted in terms of charge-transfer between the boronium cation and counter ion. Cationic and anionic organo-boron compounds. The outer electronic configuration of the boron atom in 2 1 its ground state is 2s~2p , with a first ionisation potential of 8.3e.v. Second and third ionisation potentials are 25*15 and 37.92e.v. respectively. Hence the large energy required 3+ for ionisation to Ir precludes such cationic species from the chemistry of boron. Covalent compounds of the type BX^ are well established and all monomeric compounds are planar with X-B-X bond angles -2- of 120°. However, in such compounds there remains a vacant low- lying orbital which confers pronounced Lewis acid behaviour allowing boron to achieve a coordination number of four. Anionic complexes of boron are well known, e.g. BF^, BH^, (HB(OR)^)", and illustrate the tendency of boron to achieve this coordination number. In this introduction a general review will be presented for cationic and the more important anionic species of boron, excluding the extensive and complex chemistry ofnborate anions containing only boron and oxygen. A full discussion of the borohydrides will be reserved for Part II of this thesis. Cationic organo-boron compounds; Boronium salts. Simple cationic species containing B^" are unknown, and indeed in this state the boron would contain only two electrons in the valence shell. Boronium salts containing B+ are only known in compounds containing coordinately saturated boron. The history of boronium salts extends back to 1906, but from that date until quite recently the literature contains comparatively few examples of this type of compound. Probably the first example was reported by Dilthey